1. Field of the Invention
The present invention relates to improvement of an ink jet head spraying out ink by altering the volume of an ink channel formed at a piezoelectric member and a fabrication method of such an ink jet head.
2. Description of the Background Art
As conventional ink jet heads disclosed in, for example, Japanese Patent Laying-Open Nos. 63-252750 and 2-150355, an ink jet printer head having a plurality of parallel-arranged channels that can apply pressure onto the ink is proposed.
The aforementioned conventional art is superior in that an ink jet printer head that has nozzles at high density with a relatively simple structure can be realized. However, these heads had a problem in usage application from the standpoint of fabrication since it is necessary to form the channel constituted by many trenches at high density and establish electrical wiring from respective trenches.
As a method to solve such problems, Japanese Patent Laying-Open Nos. 4-307254, 6-218918 and 6-218934 propose the method of establishing electrical interconnection using a sealing member, wherein one end of a channel which is a trench is sealed by a soldering material, a coat, or a conductive member.
The conventional art will be described with reference to FIGS. 30-33.
Referring to FIG. 30, an ink jet printer head 1 includes a piezoelectric plate 27, a cover plate 3, a nozzle plate 31, and a substrate 41. Piezoelectric plate 27 is formed of a ceramic material of lead zirconate titanate (PZT) that has ferroelectricity. Piezoelectric plate 27 is subjected to a poling process in the direction of a polarization direction 5.
Piezoelectric plate 27 has a plurality of trenches 8 formed by cutting and grinding through the rotation of a diamond cutting disk. These trenches 8 have the same depth and are arranged in parallel. A sidewall 11 which is the side plane of trench 8 is polarized in the direction of arrow 5 by the poling process.
At the inner plane of the sidewall of trench 8, a metal electrode 13 is formed by vapor deposition. In the formation process of metal electrode 13, piezoelectric plate 27 is positioned oblique to the vapor emitting direction indicated by the arrow from a target or vapor deposition source not shown, as shown in FIG. 31. Upon emission of vapor, metal electrodes 13 and 10 are formed at the upper half of the side plane of trench 8 and at the top plane of sidewall 11 by the shadow effect of sidewall 11.
Then, piezoelectric plate 27 is rotated 180 degrees, and metal electrodes 13 and 10 are formed in a similar manner. Thus, metal electrodes 13 and 10 are formed at the upper half of both side planes of trench 8 and the top face of sidewall 11. Metal electrodes 13 and 10 are formed of aluminum, nickel, and the like.
Then, a conductive member 26 is embedded in trench 8 by a dispenser 25 (refer to FIG. 3). Conductive member 26 is heated by a device not shown to be rendered solid. Conductive member 26 is formed in the vicinity of an end portion 15 of piezoelectric plate 27. Trench 8 is filled entirely with conductive member 26. Then, the excessive portion of conductive member 26 and metal electrode 10 at the top plane of sidewall 11 are removed by lapping or the like.
Cover plate 3 shown in FIG. 30 is formed of a ceramic material or resin material and the like. Cover plate 3 has an ink inlet 21 and a manifold 22 formed by grinding, cutting or the like.
As shown by the sectional configuration of trench 11 of FIG. 32, the working side plane of trench 8 of piezoelectric plate 27 and the working side plane of manifold 22 are connected by an adhesive 4 of an epoxy type or the like. Accordingly, ink jet printer head 1 is constituted by a plurality of ink channels 12 spaced apart from each other laterally and having the top face of trench 8 covered. All ink channels 12 are filled with ink.
At the end plane of piezoelectric plate 27 and cover plate 3, a nozzle plate 31 having a nozzle 32 provided corresponding to the position of each ink channel 12 is attached. Nozzle plate 31 is formed of plastic such as polyalkylene (for example ethylene), terepthalate, polyimide, polyetherimide, polyetherketone, polyethersulfone, polycarbonate, and cellulose acetate.
At the plane opposite to the working side plane of trench 8 of piezoelectric plate 27, substrate 41 is attached by an epoxy type adhesive or the like. Substrate 41 is formed with a pattern 42 of a conductive layer corresponding to the position of each ink channel 12. Pattern 42 of the conductive layer and conductive member 26 are electrically connected by wire bonding or the like.
Accordingly, metal electrode 13 located at one side plane of trench 8 and metal electrode 13 located at the other side plane are electrically connected by conductive member 26. Therefore, when voltage is applied to conductive member 26, voltage is applied at the same time to metal electrodes 13 at both sides of trench 8 through conductive member 26, whereby sidewalls 11 corresponding to the side planes of trench 8 are deformed inwards of trench 8 to spray out ink droplets.
The operation of ink jet printer head 1 will be described with reference to FIGS. 32 and 33. A driving control circuit not shown determines the spray out of ink from ink channel 12b of ink jet printer head 1 according to predetermined data. Then, a positive driving voltage V is applied to metal electrodes 13e and 13f via conductive pattern 42 and conductive member 26 corresponding to relevant ink channel 12b, and metal electrodes 13d and 13g are connected to ground.
Referring to FIG. 33, a driving electric field is generated in the direction of arrow 14b at sidewall 11b whereas a driving electric field is generated in the direction of arrow 14c at sidewall 11c. Since driving electric field directions 14b and 14c are orthogonal to the polarization direction 5, sidewalls 11b and 11c are rapidly deformed in the inner direction of ink channel 12b by the piezoelectric thickness slide effect. By this deformation, the volume of ink chamber 12b is reduced to rapidly increase the ink pressure. A pressure wave is generated to cause ink droplets to be sprayed out from nozzle 32 communicating with ink channel 12b. 
When application of driving voltage V is ceased, sidewalls 11b and 11c gradually return to their position previous to deformation. Therefore, the ink pressure within ink channel 12b is gradually lowered. As a result, ink is supplied into ink channel 12b via manifold 12 from ink inlet 21.
Thus, the center portion of the two sidewalls 11 corresponding to respective side planes of trench 8 is caused to deform inwards of trench 8 simultaneously in order to spray out ink droplets.
In the above-described ink jet printer head 1, end portion 15 of piezoelectric plate 27 blocked by conductive member 26 must be sealed completely so that ink will not be discharged from end portion 15 even when ink channel 12 is filled with ink.
In the case where conductive member 26 is formed at the trench end portion, phase-change from a liquid phase state to a solid phase state is required. The volume change caused by the phase change produces a void in conductive member 26 to result in ink leakage. Furthermore, in the case where complete sealing is not established, another member to occlude end portion 15 of trench 8 is required. This means that the fabrication method becomes more complicated.
It is noted that manifold 22 is provided at the trench attach plane of cover plate 3. Since the ink supply opening by manifold 22 is provided during the path of the ink channel, the ink channel will become longer. Also, there is a problem that the ink channel resistance is increased since the flow is altered substantially perpendicularly at the ink channel from the ink supply opening.
Also, a longer ink channel causes a higher electric resistance at the electrode portion of the sidewall, resulting in a greater load on the drive circuit. There was a problem that the size of the ink jet printer head per se is increased.
In view of the foregoing, an object of the present invention is to provide an ink jet head that can be easily fabricated, exhibits superior productivity, and that can be made compact.
In such an ink jet head, the electrode formed inside the ink chamber is extended outside the ink chamber to form a leading outside electrode. Electrical connection is to be provided between this outside electrode and an external drive circuit including the IC (Integrated Circuit) for driving. As a connection method between an outside electrode and an external drive circuit in a conventional ink jet head, the method of using a bonding wire, the method of using a TAB (Tape Automated Bonding) lead, and the method of using a flexible substrate are known, as shown in FIGS. 34-36.
Specifically, an actuator 100 is arranged on a support 110 together with an IC 130 for driving. Actuator 100 includes a substrate 103, a cover plate 123, a nozzle plate 125 and an electrode 101 inside the ink chamber. Substrate 103 is formed of a piezoelectric element, and has a plurality of sidewalls 127 arranged in a direction perpendicular to the drawing sheet. An ink chamber 122 is formed between respective partition walls 127. Cover plate 123 includes a supply opening 124 to supply ink to each ink chamber 122, and is arranged at the top plane of substrate 103. Nozzle plate 125 has a nozzle 126 from which ink is sprayed out from each ink chamber 122, and is arranged at the front side of substrate 103. Inside electrode 101 is formed in the region range of substantially the upper half of partition wall 127 in each ink chamber 122. Inside electrode 101 is formed extending towards the back side at the top plane of substrate 103. This extending portion forms an electrode 102 outside the ink chamber for leading.
Referring to FIG. 34 corresponding to the method using a bonding wire, outside electrode 102 of actuator 100 is electrically connected to the connection point of drive IC 130 through a bonding wire 111. The connection of bonding wire 111 is carried out by the Al (aluminum) wedge wire bonding technique or Au (gold) wire bonding technique. An ultrasonic wave is applied while bonding wire 111 is heated and pressed from above through a bonding capillary towards the connection point of the top plane of outside electrode 102 that is a planar plane and drive IC 130 to effect metal solid phase diffusion bonding.
Referring to FIG. 35 corresponding to the method using a TAB lead, an outer lead 112 of a TAB device is electrically connected to outside electrode 102 of actuator 100. This connection includes the steps of pressing a lead presser having a heat pressurization mechanism from above under the state where outer lead 112 of the TAB device is positioned parallel to outside electrode 102 of actuator 100, and fusing the solder that is pre-plated at the bottom plane of outer lead 112 for solder bonding. Alternatively, an ACF (Anisotropic Conductive Film) or an ACP (Anisotropic Conductive Paste) may be used instead of the solder.
Referring to FIG. 36 corresponding to the method of using a flexible substrate, an electrode 115 for connection formed on a printed circuit board 114 on which drive IC 130 is mounted is electrically connected with outside electrode 102 of actuator 100 through a flexible substrate 113. This connection has both end portions of flexible substrate 113 mounted on each top plane of connection electrode 115 and outside electrode 102, and is effected by solder bonding or using an ACF or ACP, in a manner similar to that using the TAB lead shown in FIG. 35.
A conventional method of fabricating an actuator forming an ink jet head will be described here with reference to FIG. 37.
A dry film resist is laminated and cured on a top plane 103a of a substrate 103 formed of a piezoelectric element polarized in the thickness direction (vertical direction in drawing). Using the dicing blade of a dicer, top plane 103a is half-diced from the side of front plane 103b towards back plane 103c to form an ink chamber 122 sandwiched between partition walls 127. At the middle region of substrate 103 between front plane 103b and back plane 103c, the dicing blade is raised to form an R portion 122a at the back plane side of ink chamber 122. Also, the dry film resist applied at top plane 103a to back plane 103c is cut to form a planar portion 122b. 
This dicing process is repeated in a direction parallel to front plane 103b and back plane 103c of substrate 103 to form an ink chamber array at substrate 103. Then, metal such as Al or Cu (copper) that is to become the electrode material is vapor-deposited obliquely from above substrate 103 in the longitudinal direction of ink chamber 122. By carrying out this process from two opposite directions (the direction indicated by the arrow in drawing) about ink chamber 122, inside electrode 101 is formed at respective side partition walls 127 of ink chamber 122.
At this stage, electrode 101 is formed in the area range of approximately xc2xd in the thickness direction of partition wall 127 from top plane 103a of partition wall 127 by the shadowing effect of the dry film resist and partition wall 127 in ink chamber 122. Also, oblique vapor deposition of the electrode material is carried out simultaneously at R portion 122a and planar portion 122b of ink chamber 122. Here, the thickness and opening width of the dry film resist are set so that the metal film deposited from the left and right directions overlap at planar portion 122b. Accordingly, an electrode (outside electrode) 102 is formed all over the opening portion of planar portion 122b. At R portion 122a, the electrode is formed so as to connect inside electrode 101 in ink chamber 122 with outside electrode 102 at planar portion 122b. 
Then, a cover plate 123 having a supply opening 124 as shown in FIGS. 34-36 is attached at top plane 103a of substrate 103. Nozzle plate 125 having a nozzle 126 is attached at front plane 103b of substrate 103. Thus, actuator 100 is completed.
Actuator 100 formed as described above carries out shear mode driving by applying a potential of opposite phase to each other to respective inside electrodes 101 formed in an adjacent ink chamber 122 with partition wall 127 therebetween. More specifically, partition wall 127 having a potential of opposite polarity applied to respective side planes exhibits shearing deformation in an angle bracket configuration at the boundary between the region where inside electrode 101 is formed and the region where inside region 101 is not formed. This shearing deformation of partition wall 127 alters the volume of ink chamber 122, whereby the ink pressure in ink chamber 122 changes to spray out ink droplets from nozzle 126 arranged at the front plane 103b side of ink chamber 122.
In the conventional ink jet head of the above-described structure, the active region that contributes directly to the ink discharge of ink chamber 122 formed in actuator 100 is limited to the side of front plane 103b in front of supply opening 124 (the side where nozzles are formed). The back plane 103c side including supply opening 124 is the region to supply ink into ink chamber 122. R portion 122a and planar portion 122b are the regions to connect inside electrode 101 facing each other in ink chamber 122 to form one outside electrode 102 which serves to electrically connect an external electrode that conducts with drive IC 130. According to the structure of such an ink jet head, the portion other than the active region that contributes to ink discharge is extremely great to cause increase in the material cost. There was a problem that an economic ink jet head could not be fabricated.
It is also necessary to extend inside electrode 101 as far as planar portion 122b on substrate 103 that is based on a piezoelectric element such as of PZT that has high permittivity. Therefore, the electrical capacitance of substrate 103 is increased to dampen the waveform of the driving voltage that is to be applied in the drive of actuator 103. There was a problem that high speed print out by high speed driving cannot be carried out easily. Although this dampening of the waveform of the driving voltage can be alleviated by raising the applied voltage, this increase of the applied voltage will cause a great amount of generated heat by the drive of actuator 100. The viscosity of ink will change by the rise in temperature of actuator 100. Thus, there was a problem that accurate printing cannot be carried out stably. There is also a problem that the cost of driving IC 130 to apply a high voltage is increased. Furthermore, there was a problem that power consumption cannot be reduced.
In view of the foregoing, the electrical capacitance of substrate 103 at the region other than the active region is rendered to a negligible level by forming in advance a low dielectric film between the piezoelectric element and inside electrode 101 at the region other than the active region of inside electrode 101 of actuator 100. However, an expensive ECR-CVD (Electron Cyclotron Resonance Chemical Vapor Deposition) device is required to form an Sixe2x80x94N film of low permittivity by a process of low temperature on PZT that has a low Curie point of approximately 200xc2x0 C. The fabrication cost will become so high that an economic ink jet head cannot be fabricated.
Japanese Patent Laying-Open No. 9-94954 discloses a structure of avoiding the formation of the region of a supply opening 214a and the extension of an inside electrode 213 in the longitudinal direction of the piezoelectric element. According to this structure, ink is supplied into an ink chamber 214 through a supply opening 214a provided at the trailing end portion of the active region of substrate 210. Inside electrode 213 formed in ink chamber 214 extends from a discharge hole 212 towards supply opening 214a, and is formed integrally with an outside electrode 215 extending towards the trailing end plane of substrate 210. Inside electrode 213 is electrically connected with an electrode 217 conducting with drive IC 216 in outside electrode 215.
According to this structure, the material cost of the piezoelectric element can be reduced since there is no region other than the active region of actuator 200. However, there is a problem that the electrical capacitance of substrate 210 is increased. Furthermore, since inside electrode 213 is bent 90xc2x0 at the side plane of actuator 200 so as to extend outside electrode 215, outside electrode 215 cannot be formed simultaneously during the oblique vapor deposition process of forming inside electrode 213 in the wafer status.
Inside electrode 213 and outside electrode 215 at the side plane of actuator 200 will be formed after each actuator 200 is cut out (diced into a small piece) from the wafer. However, in order to lead out the two inside electrodes 213 facing each other in ink chamber 214 while ensuring an electrically conductive state, oblique vapor deposition is required from at least two further directions. In order to isolate outside electrode 215 extending to the side plane of actuator 200 for each ink chamber 214, a patterning process must be carried out in advance. In the case where patterning is not carried out, an electrode isolation process by dicing or using a YAG laser is required after the draw out of the bare electrode. Since the fabrication step becomes more complicated, the productivity is poor and the yield is degraded. There was a problem that the production cost is increased.
Although the outer wiring can be formed also by plating, a patterning step or an electrode isolation step is required as by the vapor deposition technique. Thus, there was a problem that the processing step becomes more tedious. There is also the possibility that the outgoing electrode is disconnected at the bending portion from ink chamber 214 at the side plane of actuator 200 by a subsequent process or handling. There was a problem that the production yield as well as the environment reliability are degraded.
In view of the foregoing, another object of the present invention is to provide an ink jet head and a fabrication method thereof that can prevent increase of a substrate area without raising the cost caused by the usage of an extensive fabrication apparatus, complication of the fabrication step, and degradation of the yield due to disconnection of the electrode, and that can prevent increase of the material cost as well as prevent increase of the electrical capacitance of the substrate to allow stable high speed print out in high accuracy without increase of the heat generated in the actuator, and a method of fabricating such an ink jet head.
An ink jet head of the present invention causes deformation of partition walls to discharge ink from an ink chamber by having an inside electrode formed at each inner side plane of one pair of partition walls sandwiching a trench-like ink chamber, and electrically connected to an external drive circuit, and applying a driving pulse from the external drive circuit to the inside electrode in the ink chamber. The ink jet head of the present invention includes a substrate having a partition wall constituted by forming an ink chamber trench located from one end plane to the other end plane. The end plane of the inside electrode located at only the interior of the ink chamber trench is exposed at the other end plane. The external drive circuit is electrically connected to the inside electrode at the other end plane. An ink supply opening to supply ink into the ink chamber is provided at the other end plane side.
According to such a structure, the ink supply opening is provided at the other end plane side. Therefore, it is not necessary to completely seal the other end plane of the piezoelectric plate with a conductive member. The reliability and productivity are increased.
Since an ink supply opening is not provided in the path of the ink channel, the length of the ink channel can be shortened. A compact ink jet printer can be realized. Also, the electrical resistance of the inside electrode portion can be reduced to alleviate the load of the drive circuit.
The ink flow is substantially linear from the supply opening to the ink channel. Therefore, a flow of no resistance can be provided to allow ink to be discharged stably.
The inside electrode is located only inside the ink chamber trench, and has its end plane exposed at the other end plane of the substrate. Therefore, the lead out of the inside electrode to outside the ink chamber trench for mounting in the conventional device is dispensable in the present invention. Any portion other than the active area of the actuator is practically no longer required, so that the material cost can be reduced. Also, reduction of the electrical capacitance allows improvement of the driving frequency. Therefore, high speed print out can be realized. Since the breakdown voltage of the drive IC can be lowered due to the reduction of the driving voltage, the cost of the drive IC as well as the power consumption for driving can be reduced.
The above ink jet head preferably comprises a cover plate attached at the surface of the substrate where the ink chamber trench is formed. The ink jet head is characterized in that the ink supply opening is provided at least at the cover plate side.
By forming the ink supply opening at the cover plate side, ink can be introduced straight into each ink channel along the cover plate.
Preferably, the above ink jet head further comprises a filling member formed between the pair of partition walls at the other end plane of the ink chamber trench.
Preferably, the above ink jet head further comprises a protection film to protect the connection portion where the inside electrode is electrically connected to the external drive circuit.
By providing insulative protection on the connection portion by the protection film, the connection portion can be protected in the case where conductive ink is used.
In the above ink jet head, the filling member is formed of a conductive material, and the external drive circuit and the inside electrode are electrically connected via the filling member.
In the above ink jet head, the filling member is preferably a conductive resin that occludes the other end plane of the ink chamber trench between a pair of partition walls.
According to such a structure, the other end plane of the ink chamber trench is occluded by a conductive resin. The conductive resin prevents ink leakage from the other end plane in the ink discharge direction of the ink chamber. Almost all the region in the ink chamber serves as an active region to output ink. Therefore, the material cost of the piezoelectric element forming the ink chamber is reduced. Also, the electrical capacitance of the substrate will not be increased.
In the above ink jet head, the filling member preferably includes a conductive filler of a predetermined configuration formed of a predetermined material.
According to such a structure, the other end plane in the direction of ink discharge of the ink chamber between the pair of partition walls is occluded by the filling member of a conductive material including a conductive filler of a predetermined configuration formed of a predetermined material. Therefore, the material of the conductive filler can be selected depending upon whether improvement of the driving frequency or reduction of the cost is to be given weight. The configuration of the conductive filler can be selected depending upon whether the connection resistance is to be reduced by the effective damage of the oxidation film of the electrode or by the increase of the contact area per unit volume. By using a conductive resin including such a conductive filler, connection is established between the electrode inside the ink chamber and the external drive circuit in a state where the function corresponding to the usage application is realized.
As the material of the conductive filler, Au or Ag can be used.
According to such a structure, the connection resistance between the electrode inside the ink chamber and the external drive circuit can be suppressed to a low level. The waveform of the driving voltage to drive the actuator will not be dampened. The driving frequency can be increased to correspond to high speed print out.
Furthermore, as the material of the conductive filler, Ni, Cu or carbon can be used.
By such a structure, a conductive resin can be constituted by a relatively economic material to allow reduction of the cost.
Regarding the configuration of the conductive filler, an acute portion can be provided at the outer peripheral portion.
According to such a structure, the oxide film at the surface of the electrode can be broken effectively by the contact with the conductive filler during the filling step of the region between one pair of partition walls with the conductive resin. The contact resistance between the electrode and the external drive circuit can be reduced.
Furthermore, substantially sphere configuration can be employed as the configuration of the conductive filler.
By such a structure, the density of the conductive filler in the conductive resin can be maximized to increase the contact area per unit volume of conductive resin. Accordingly, the contact resistance between the electrode and the external drive circuit can be reduced.
The greatest diameter of the conductive filler can be set to less than the distance between one pair of partition walls of the ink chamber. By such a structure, the conductive resin including the conductive filler can reliably fill the pair of partition walls.
The glass transition point of the resin material can be set to at least 60xc2x0 C.
By such a structure, sufficient reliability can be achieved at the storage temperature region and usage temperature region of the ink jet head.
In the above-described ink jet head, the filling member preferably is solder that occludes the other end plane of the ink chamber trench between each inside electrode formed at each side plane of the pair of partition walls.
In such a structure, the other end plane of the ink chamber trench is occluded by solder between the pair of partition walls. Therefore, sufficient strength is achieved at the connection portion when the inside electrode is electrically connected to the external drive circuit. Thus, the reliability of the connection state is improved.
The solder can be Sn base solder.
By such a structure, electrical connection can be established between the electrode and the external drive circuit using solder that is relatively economic and readily available. Therefore, the cost can be reduced. The element to be added as well as the added amount can be changed easily. The melting temperature can be easily adjusted depending upon the temperature condition in the connection step between the electrode and the external drive circuit. Therefore, change in the fabrication step and specification can be easily accommodated.
The melting point of the solder can be set to at least 80xc2x0 C.
By such a structure, sufficient reliability can be achieved at the storage temperature region and usage temperature region of the ink jet head.
According to above-described ink jet head, the filling member has the exposed portion out of the ink chamber trench electrically connected to the connection terminal of the external drive circuit.
By such a structure, the exposed portion from the ink chamber of the conductive material that occludes the other end plane of the ink chamber trench between the pair of partition walls is electrically connected to the connection terminal of the external drive circuit. The connection terminal of the external drive circuit will not form direct contact with the substrate where the ink chamber is formed. The connection portion between the inside electrode and the external drive circuit will not be affected by the deformation of the partition wall caused by the application of a driving voltage to the electrode.
In the above-described ink jet head, the filling member is preferably the connection terminal of the external drive circuit inserted to the other end plane of the ink chamber trench.
In such a structure, electrical connection is established between the inside electrode and the external drive circuit by inserting the connection terminal of the external drive circuit to the other end plane of the ink chamber trench. Therefore, the electrode inside the ink chamber can be electrically connected to the external drive circuit readily.
In the above-described ink jet head, the filling member preferably includes the conductive resin occluding the other end plane of the ink chamber trench between each inside electrode formed at each wall of the pair of partition walls, and the connection terminal of the external drive circuit inserted to the other end plane of the ink chamber trench.
In such a structure, the connection terminal of the external drive circuit is inserted into the other end plane of the ink chamber trench filled with the conductive resin. Therefore, the electrode in the ink chamber is electrically connected to the external drive circuit through the connection between the conductive resin and the conductive terminal.
In the above-described ink jet head, the conductive resin occluding the region between the electrodes in the ink chamber is preferably a conductive adhesive.
In such a structure, electrical connection is established at the other end plane of the ink chamber trench via a conductive adhesive between the inside electrode and the connection terminal of the external drive circuit. Therefore, the connection terminal of the external drive circuit is inserted into the other end plane of the ink chamber trench without direct contact with the partition wall of the ink chamber. Therefore, the partition wall will not be damaged. Furthermore, the impact at the time of inserting the external terminal of the external drive circuit to the other end plane of the ink chamber trench is alleviated by the conductive adhesive to prevent occurrence of strain caused by vibration.
Preferably in the above-described ink jet head, an anisotropic conductive adhesive can be employed as the conductive adhesive.
By such a structure, the application of the anisotropic conductive adhesive at the other end plane including the partition wall of the ink chamber allows mechanical connection between the substrate and the external drive circuit at the same time of the electrical connection between the inside electrode and the connection terminal of the external drive circuit.
Preferably in the above-described ink jet head, the connection terminal of the external drive circuit is deformed by the abutment with the conductive resin when inserted into the other end plane of the ink chamber trench.
Therefore, the impact generated during the insertion of the connection terminal of the external drive circuit to the other end plane of the ink chamber is buffered by the connection terminal to prevent damage of the partition wall and generation of strain caused by vibration. A similar effect can be obtained when either or both of the inside electrode and the filling member exhibit deformation at the time of insertion of the filling member.
Preferably in the ink jet head, the other end plane of the ink chamber trench has a guide portion formed. The guide portion is configured to introduce the filling member inside the ink chamber trench.
In such a structure, the filling member is introduced into the ink chamber trench by the guide portion at the time of insertion to the other end plane of the ink chamber trench. This ensures the insertion of the filling member in the ink chamber trench.
The guide portion may have an inclining plane at the other end plane in which the opening diameter becomes smaller from the edge of the ink chamber trench towards the interior.
By such a structure, the abutment of the connection terminal of external drive circuit against the inclining plane allows the guidance of the connection terminal of the external drive circuit inside the ink chamber along the inclining plane. The process of inserting the connection terminal of the external drive circuit into the ink chamber can be simplified.
The above-described ink jet head preferably comprises a connection conductor layer electrically connected to the electrode inside the ink chamber. The end plane of the connection conductor layer located only inside the ink chamber trench is exposed at the other end plane. Electrical connection with the external drive circuit is established at the end of the exposed connection conductor layer.
Accordingly, both of the electrodes forming a pair inside the ink chamber can be electrically connected by connecting the external drive circuit to just one of the inside electrodes facing each other with the ink chamber trench therebetween.
In the above-described ink jet head, the area of the cross section of the end plane of the inside electrode exposed at the other end plane is preferably at least 7xc3x9710xe2x88x925 mm2.
Accordingly, in the connection process with the electrode electrically connected to the IC for driving the ink jet head carried out subsequently, sufficient reliability can be achieved in the electrode connection using an ACA (Anisotropic Conductive Adhesive) or NCA (Non-Conductive Adhesive).
Preferably in the above-described ink jet head, at least either the inside electrode or the connection conductor film has a metal film plated at the surface.
It is necessary to ensure sufficient thickness of the electrode since the inside electrode and the connection conductor layer are employed as the electrode for connection with the external drive circuit. The formation of a metal film through a vacuum process such as vapor deposition and sputtering is disadvantageous in productivity since the throughput is slow. However, by forming only the seed layer for plating thin by the vacuum process and forming a metal film of the desired thickness by plating, the productivity can be improved. The film quality of the metal film per se is uniform. The internal stress can be alleviated to reduce the defect of metal film peeling. An economic ink jet head stable in quality and high in reliability can be realized.
The above-described ink jet head preferably includes a filling member so as to occlude the other end plane side of the ink chamber trench between the pair of partition walls. The filling member includes either a conductive resin or an insulative resin.
Since a predetermined region in the ink chamber trench is filled with a conductive resin or insulative resin, the strength of the channel wafer is increased to alleviate damage in the subsequent dicing process into small pieces. The production yield can be improved. Therefore, an economic ink jet head can be realized.
In the case where a conductive resin is employed, the pair of inside electrodes in the same ink chamber trench can be electrically connected by the conductive resin. Furthermore, since the cross section plane of the conductive resin can be used as the connection electrode with the external drive circuit, a large connection area can be readily provided to allow favorable connection stability. In the case where an insulative resin is employed, fillers that have a relatively low coefficient of linear expansion such as silica filler and alumina filler can be dispersed into the additive to the resin. Therefore, the low coefficient of linear expansion of the piezoelectric element can be easily met. Damage of the piezoelectric element caused by heat stress and the like can be prevented. The environment reliability is improved.
Preferably in the above-described ink jet head, the filling member has at least the property of either an elastic modulus of not more than 10 GPa under an environment of 100xc2x0 C. and below, or a coefficient of linear expansion of not more than 50 ppm/xc2x0 C. under an environment of 100xc2x0 C. or below.
Accordingly, the heat stress between the piezoelectric element and the filling member can be alleviated by the elastic deformation of the filling member when the elastic modulus of the filling member is not more than 10 GPa. When the coefficient of linear expansion of the filling member is not more than 50 ppm/xc2x0 C., the heat stress can be reduced. Therefore, an ink jet head superior in environment reliability can be provided.
Preferably in the above-described ink jet head, each of the inside electrodes formed at the inner side plane of one pair of partition walls is electrically connected by a connection conductor layer formed along the inner wall plane of the ink chamber trench.
When each of the inside electrodes formed at each inner side plane of one pair of partition walls is not electrically connected by the connection conductor layer, i.e., electrically separated, an outside electrode conducting with the external drive circuit must be connected to the end plane of each inside electrode when the electrode conducting with an internal drive circuit is to be connected with an ACA. However, as long as each of the inside electrodes forming a pair is electrically connected by the connection conductor layer, the external electrode of the external drive circuit only has to be connected to the end plane of one of the inside electrodes using at least one ACA conductor particle in the connection of the external electrode conducting with the external drive circuit through an ACA. Therefore, the density of the scattering conductor particles of the ACA can be reduced, which allows reduction in the cost of the ACA material and is advantageous from the standpoint of insulation with respect to the inside electrode of an adjacent ink chamber trench. Accordingly, the pitch can be reduced. Thus, an economic ink jet head that allows print out at high accuracy can be provided.
A method of fabricating an ink jet head of the present invention includes the steps of forming a plurality of ink chamber trenches in a predetermined pitch at a top plane of a channel wafer of a piezoelectric element subjected to a polarization process in the thickness direction, forming an inside electrode independent to each other at each facing plane of the plurality of ink chamber trenches, attaching a cover wafer at a top plane of the channel wafer, cutting and dividing the attached channel wafer and cover wafer in a direction crossing the longitudinal direction of the ink chamber trench, and forming an ink supply opening at the cut plane.
Conventionally, the actuator is large in size and has a complicated structure. Also, the actuator had the inside electrode drawn out from the ink chamber trench for connection with an external drive circuit. In contrast, according to the fabrication method of the present invention, the channel wafer and cover wafer are cut after the inside electrode is formed in the ink chamber trench to expose the end plane of the inside electrode at the cut plane. Therefore, the external drive circuit can be electrically connected to the exposed end plane of the inside electrode without having to draw the inside electrode out from the ink chamber trench. Also, an ink supply opening can be formed at the cut plane.
Since it is not necessary to draw out the inside electrode out from the ink chamber trench, the portion other than the active area of the actuator is practically dispensable. Therefore, the material cost can be reduced. Also, since the driving frequency can be improved by reduction of the electrical capacitance, high speed printing can be realized. Reduction in the driving voltage allows the breakdown voltage of the drive IC to be reduced. Therefore, the cost of the drive IC and the power consumption can be reduced.
Furthermore, the fabrication step can be simplified since it is not necessary to form an actuator of a complicated structure.
Preferably, the ink jet head fabrication method further includes the step of forming in the fabrication method of an ink jet head, the step of forming a filling member preferably includes the step of fusing solder paste which is the conductive material by light energy.
According to the present method, the other end plane of the ink chamber in the direction of ink discharge is occluded using the fused solder paste used by local heating through light energy. Therefore, depolarization caused by excessive heat load at the active region of the ink chamber will not occur. The ink discharge performance will not be degraded.
In the above-described fabrication method of an ink jet head, the step of forming a filling member preferably includes the step of cooling the portion of the channel wafer where the filing member is not inserted.
By such a structure, the portion that becomes the active region of the ink chamber trench is forced to cool during the occlusion step of the other end plane of the ink chamber trench by the conductive material. Therefore, heat load will not act on the active region of ink chamber. Reduction in the performance of the ink discharge caused by depolarization can be reliably prevented.
The fabrication method of an ink jet head further includes the step of forming a conductor layer for connection along an inner wall plane of the ink chamber trench. The inside electrode is formed so as to come into contact with that connection conductor layer.
Accordingly, the connection with the electrode conducting with an external drive circuit effected subsequently can exhibit high mounting reliability by forming a thick metal film carried out at another step. Also, the throughput of the vacuum process is increased to improve the productivity since the electrode does not have to be made as thick as the electrode for driving. Furthermore, power consumption can be reduced without increasing the driving load of the active area of the ink jet head driven in a shear mode.
The above-described fabrication method of the ink jet head preferably includes the step of forming a filling member so as to fill a predetermined region between the inside electrodes facing each other in each of the plurality of ink chamber trenches. The channel wafer and cover wafer, after being attached, are cut at the position where the filling member is cut.
Since the filling member formed of a conductive resin or insulative resin is filled in the ink chamber, the strength of the channel wafer is increased to alleviate damage in the subsequent dicing process into small pieces. The production yield is improved to allow an economic ink jet head. In the case where a conductive resin is employed, the plurality of drive electrodes in the same ink chamber can be integrated by the conductive resin filling the ink chamber. Since the cross section of the conductive resin can be used as the electrode for connection with an external circuit, a large connection area can be obtained. The stability of connection is superior. In the case where an insulative resin is employed, a large amount of filler of a relatively low coefficient of linear expansion such as a silica filler or alumina filler can be dispersed into the additive of the resin. Therefore, the coefficient of linear expansion of the piezoelectric element can be easily met. Furthermore, damage of the piezoelectric element caused by heat stress and the like can be prevented. An ink jet head superior in environment reliability can be realized.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.